program Problem3;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var n, k: integer;
    i: integer;

begin
  Readln(n);
  k:=0;
  If n mod 2=0 then
    For i:=1 to n div 2 do
      k:=k+(2*i);
  If n mod 2=1 then
    For i:=1 to n div 2 do
      k:=k+(2*i+1);
  Writeln(k);
  Readln;
end.
